The invention relates to a method for the characterization of semiconductor surfaces by means of surface patterns which are generated by respective melting and partial vaporization of a surface segment of the semiconductor surface by means of a laser beam.
It is known to provide semiconductor surfaces with surface patterns for the characterization thereof by means of laser radiation, and wherein arrangement of the surface patterns with respect to one another results in the formation of desired symbols, such as letters or numerals. Such characters should be rich in contrast and permanent-namely, they should be recognizable in a trouble-free manner, for example, even after several high temperature- and/or oxidation treatments of the respective semiconductor surface without any impairment of their surface quality.
According to a known method, the desired location of the semiconductor surface to be characterized is irradiated by means of high-powered laser pulses, which cause the semiconductor material of the irradiated surface segment to melt, and then cause the melted surface material to almost completely vaporize. In this manner, surface patterns in the shape of dot-like recesses are obtained, which by themselves, are rich in contrast and permanent, but are always surrounded by a rim of melted beads and random deformities (so-called "slag"). In any subsequent processes, for example, an oxidation process, very small particles can break off from this slag, and be subsequently deposited on the semiconductor surface. This, in turn, may finally lead to errors in the semiconductor devices subsequently produced, and, therefore, may lead to a loss in the yield.
This disadvantage is avoided by another known method, in which in the surface segment of the semiconductor material irradiated by the laser pulse is only melted and is no longer vaporized. The so-obtained dot-shaped surface patterns are, it is true, free from any slag, but are poor in contrast, and in view of their short depth, are not very permanent.
A further method, in which complete letters or numerals are generated in a semiconductor surface with the aid of masks by means of a single laser pulse, yields only a non-uniform lettering, which is poor in contrast.